Systems to perform time synchronization among a plurality of devices are known. For example, a device that transmits a request signal for time adjustment to another device with constant periods, and performs time synchronization, using a response signal, to the request signal, received from the another device is disclosed. Further, a technology to set a synchronization period to be larger than initial setting, when an error between a time after time synchronization and a time of a server falls within a predetermined value, is disclosed.
However, conventionally, a time required to reach synchronization accuracy of a target level from the activation of the device cannot be regulated, and time synchronization that satisfies the target level sometimes takes a time.